The U.S. Fish and Wildlife Service is trying to wipe out rats on an uninhabited islet using fish-flavored grain pellets brimming with poison.
The non-native Polynesian rats are killing rare seabirds, plants and seeds on Mokapu, which lies off Molokai, according to the Fish and Wildlife Service. The island is a state seabird sanctuary and is considered especially at risk because of Hawaii’s remoteness and unique flora and fauna.
“We aren’t going to declare victory until we haven’t detected rats over a couple of seasons,” said Mindy Wilkinson, invasive species coordinator for the state Department of Land and Natural Resources.
The only other uninhabited Hawaiian island with rats detected on it is Lehua, northwest of Kauai, which could be next for the program, Wilkinson said.
Mokapu Island hosts the wedge-tailed shearwaters or uau kani, red-tailed tropicbirds or koaeula and white-tailed tropicbirds or koae kea, as well as 11 of the last 14 hoawa plants in the wild. There’s also a small population of uncommon loulu lelo palms. All of these the rats eat.
Wilkinson said biologists have made note over the years how, unlike other neighboring islets, Mokapu is short on palms and other plants, which they attribute to hungry rats.
A biologist will be sent out to the island this summer to see how many rats were killed, said Ken Foote of the Fish and Wildlife Service.
Volcanic Helicopters from Hilo sprayed Mokapu Island twice in February with the pellets, each of which contain 50 parts per million of diphacinone. Sample tests taken from minnows, grown fish and seawater near the island found no trace of the poison last month.
Fish and Wildlife Service officials reported using safeguards to ensure that the bait pellets didn’t land in the ocean, such as dropping them during a low wind period with no rain and using a global positioning system to make sure they hit their targets. Marine sampling results can be viewed online at http:// www.hawaii.gov/dlnr.
The poison has been around for years and is designed to kill rodents. It is an anti-coagulant that causes massive internal hemorrhaging and reportedly a painless death.
It is dangerous to humans and other mammals if eaten or inhaled, but diphacinone is categorized as slightly to moderately toxic to birds and fish, according to Cornell University’s Pesticide Management Education Program.
Wilkinson said that in trials on the Big Island, birds and fish ignored the waxy pellets, which dissolved slowly with no measurable effects on the environment.
For this two-year project to get under way, the participants had to complete an environmental assessment to ensure that it wouldn’t harm the rare plants and animals that the poison is meant to protect. The project also required several public meetings on Molokai.
The Polynesian rat is the third most common rat in the world and was introduced across the Pacific Ocean and Southeast Asia by trading ships. The rats are omnivores and are known for their ability to deforest a region because they love to feed on palm nuts.
Project coordinators can monitor only the island’s ridges because it is so inaccessible. Other partners include the U.S. Department of Agriculture, the Maui Invasive Species Committee, The Nature Conservancy, Hacco Inc. and United Agriproducts.
Mokapu is a tiny but steep island just east of the Kalaupapa peninsula. This is the first time aerial application has been done off the Hawaiian Islands, although the process has been used in other parts of the world since the 1990s, said Chris Swenson, Fish and Wildlife Service Pacific Islands Coastal Program coordinator.
The bait had to be applied twice to ensure that it was evenly distributed, since the rats must eat it multiple times before dying.
Diphacinone is considered safer than other compounds used by the government in the past, according to the Fish and Wildlife Service.
“The success of the Mokapu Island rat eradication project will provide natural resource managers throughout the state access to a proven method of bait application using a less toxic and more environmentally friendly rodenticide,” said Project Manager Peter Dunlevy.
However, the project will be considered a success only if and when all the rats are gone.
• Chris Hamilton can be reached at chamilton@mauinews.com.
